BLASTOCLADIALES 609 



when the zoospores are emerging from the sporangium and when they 

 are nearing the end of their period of swarming. The body of the spore 

 at these times may elongate slightly, become strongly vacuolate, and 

 produce broad irregular anterior and lateral pseudopodia. 



The flagellum of the zoospore in Allomyces, already determined by 

 Couch (1941) to be of the whiplash type, has been carefully examined 

 by Manton, et al. (1952), see p. 10. They confirmed Ritchie's (1947) 

 observations as to the flagellum's fibrillar nature. 



Cantino and Horenstein (1954) have presented careful experimental 

 and observational evidence to the effect that a cytoplasmic transfer may 

 take place between swarmers of Blastocladiella. In a pigmented mutant 

 strain of B. emersonii a certain minimum percentage of its swarmers 

 would pair up and undergo some sort of exchange with normal, color- 

 less swarmers of the species. Furthermore, such mutant swarmers might 

 then repeat the process with other swarmers of B. emersonii, so that a 

 single normal swarmer of the latter may be successively approached, 

 in turn, by several from the mutant. These investigators were also able 

 to demonstrate that cytoplasmic bridges formed between such swarmers 

 but that no changes occurred in their nuclei. Cantino and Horenstein 

 conclude that if the bridges were functional, a cytoplasmic rather than 

 a nuclear exchange mechanism was involved. They postulate that this 

 transfer of cytoplasmic factors may chiefly be a unilateral one, either 

 from the mutant to the normal B. emersonii or vice versa. Further, they 

 also discuss the significance of this paramecium-like behavior to the 

 distribution of a physiologically active cytoplasmic material which they 

 believe governs the growth pattern in Blastocladiella as earlier described 

 by Cantino and Hyatt (1953a). Their hypothesis lends support to the 

 contentions by Emerson (1950) and Cantino and Hyatt (op.cit). that 

 the expression of "sex" in Blastocladiella is not genotypically controlled. 



The zoospores after a varying period of motility come to rest, round 

 off, and apparently absorb the flagellum into the body. Eventually a 

 slender germ tube appears, which branches distally to form the first 

 elements of the holdfast system. The body of the spore enlarges, the 

 region opposite the point of origin of the rhizoids elongates rapidly, 

 and there is either produced the reproductive rudiment or the basal cell. 

 In contrast to the Chytridiales, germination is bipolar in nature. Subse- 



